ATtiny261A datasheet(100/292 Pages) ATMEL

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8197A–AVR–10/09

ATtiny261A/461A/861A

in a constantly high or low output (depending on the polarity of the output set by the COM1x1:0

bits.)

A frequency (with 50% duty cycle) waveform output in fast PWM mode can be achieved by set-

ting the Waveform Output (OCW1x) to toggle its logical level on each Compare Match

(COM1x1:0 = 1). The waveform generated will have a maximum frequency of fOC1 = fclkT1/4 when

OCR1C is set to three.

The general I/O port function is overridden by the Output Compare value (OC1x / OC1x) from

the Dead Time Generator, if either of the COM1x1:0 bits are set and the Data Direction Register

bits for the OC1X and OC1X pins are set as an output. If the COM1x1:0 bits are cleared, the

actual value from the port register will be visible on the port pin. The Output Compare Pin config-

urations are described in Table 12-3.

12.8.3

Phase and Frequency Correct PWM Mode

The Phase and Frequency Correct PWM Mode (PWM1A/PWM1B = 1 and WGM11:10 = 01) pro-

vides a high resolution Phase and Frequency Correct PWM waveform generation option. The

Phase and Frequency Correct PWM mode is based on a dual-slope operation. The counter

counts repeatedly from BOTTOM to TOP (defined as OCR1C) and then from TOP to BOTTOM.

In non-inverting Compare Output Mode the Waveform Output (OCW1x) is cleared on the Com-

pare Match between TCNT1 and OCR1x while upcounting, and set on the Compare Match while

down-counting. In inverting Output Compare mode, the operation is inverted. In complementary

Compare Output Mode, the Waveform Ouput is cleared on the Compare Match and set at BOT-

TOM. The dual-slope operation has lower maximum operation frequency than single slope

operation. However, due to the symmetric feature of the dual-slope PWM modes, these modes

are preferred for motor control applications.

The timing diagram for the Phase and Frequency Correct PWM mode is shown on Figure 12-13

in which the TCNT1 value is shown as a histogram for illustrating the dual-slope operation. The

counter is incremented until the counter value matches TOP. When the counter reaches TOP, it

changes the count direction. The TCNT1 value will be equal to TOP for one timer clock cycle.

The diagram includes the Waveform Output (OCW1x) in non-inverted and inverted Compare

Output Mode. The small horizontal line marks on the TCNT1 slopes represent Compare

Matches between OCR1x and TCNT1.

Table 12-3.

Output Compare Pin Configurations in Fast PWM Mode

COM1x1

COM1x0

OC1x Pin

Disconnected

OC1x

Disconnected

OC1x

Disconnected

OC1x

ATtiny261A Datasheet(PDF) 100 Page - ATMEL Corporation

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